Sleeping the full eight hours usually advised by doctors might not be necessary for everybody, according to a new study, which suggested there’s a gene that dictates how much sleep a person needs.

A researching team at the University of California, headed by Ying-Hui Fu, analyzed the genes of 12 members of a family that sleeps as little as 4.5 hours per night without feeling tired. They found they had a mutation in a gene called ADRB1.

“We all spend about one-third of our lives in the state of sleep,” Fu said. “In fact, considering how important sleep is to our well-being, it’s astonishing that we know so little about how sleep is regulated.”

The team bred rats with the same mutation, which slept about 55 minutes less per day. This correlated with altered activity in a brain region called the dorsal pons that is known to regulate sleep.

In normal rats, ADRB1-expressing brain cells were found to be inactive during most sleep stages, but active when they were awake. In the mutant ones, these cells were even more active during waking hours. The researchers also found they could wake up sleeping rats by artificially activating these ADRB1-expressing brain cells.

The results suggest that ADRB1-expressing brain cells promote wakefulness and that variations in the ADRB1 gene influence how long we can stay awake for each day, said Fu. Her team has previously found that mutations in other genes like DEC2 also make people need to sleep less.

These mutations don’t seem to be associated with any negative health consequences. “Most natural short sleepers are very happy about their sleep pattern – they usually fully take advantage of their extra time,” Fu told New Scientist.

The researchers think the ADRB1 and DEC2 mutations must have emerged recently in human history and haven’t had time to spread widely yet. “The 8-hour norm has been the standard for a long time, but somehow a few new mutations occurred recently and produced this seemingly advantageous trait,” Fud said.

While this is newly discovered mutated gene contributes to short sleep, the study highlighted it’s probably not the only one. There are likely more unrecognized genes and regions of the brain that tell our bodies when to go to bed and rise in the morning.

“Identifying genes, and mutations, that cause people to sleep less naturally without significant negative impact lays the groundwork for scientists to investigate how our sleep homeostasis and efficiency is regulated at the molecular and neuronal levels,” Fu says.